In the pressing of glass articles, such as culinary ware, TV bulb components, and other vessels, a major consideration is the control of heat distribution and removal in order that the surfaces which form the glass articles are neither too hot nor too cold. If the surfaces become too hot, sticking of the glass may occur to the mold, and if the surfaces become too cold, a crizzling or checking of the glass may occur.
Various methods have been utilized in the past to control the cooling of mold surfaces including the utilization of compressed and fan air as shown in U.S. Pat. Nos. 2,688,823 and 4,032,317, and the utilization of water cooling as shown in U.S. Pat. Nos. 3,054,220 and 3,468,654. The use of fan air or compressed air for cooling mold equipment not only limits production speeds due to the limited degree of cooling obtained thereby, thus rendering such air cooling systems to be rather costly, but also results in excessive noise due to the high volume and velocity of air required. Water cooled mold systems, on the other hand, which include both contained or enclosed systems, and exposed or open spray-type systems, have not been entirely satisfactory. The closed system with its attached water supply does not readily lend itself for use with revolving molds, and further there is a tendency for a film to form which insulates further cooling; and the open system creates a problem of steam which is detrimental to both the worker and apparatus alike, plus the fact there is the requirement for collecting the spent cooling water.
Glass articles, such as for example vessels and other culinary ware, are customarily formed by placing a charge of hot molten glass into a mold cavity and then introducing a plunger into the charge of glass so as to press-form a finished article between the mold and the plunger.
The repeated exposure of the mold and plunger, as they come into contact with the molten glass during the forming operation, causes the temperatures thereof to rise, and therefore it is imperative that they be cooled to within acceptable working ranges. If the mold, for example, is not cooled sufficiently, it will reach a temperature at which the glass will begin to fuse to the metal interior forming surface of the mold, which will of course necessitate the stoppage of the forming equipment in order to repair the damage caused by the fusing of the glass to the mold part. If the temperature of the mold is not maintained, or if permitted to fall below a predetermined level, wrinkles, checks and other imperfections can result in the finished article. Therefore, it is evident that there exists a desirable working range within which the molding parts should be maintained.
The present system includes the use of a liquid coolant, such as water, within a closed system which takes advantage of the large latent heat of vaporization as the coolant adjacent the forming wall boils and evaporates, thus rendering more effective heat transfer and thereby allowing for increases in production speeds. However, as previously mentioned, nucleate boiling is effected while film boiling is inhibited, thus facilitating the desired high rates of heat removal. Nucleate boiling is the ordinary boiling of a fluid such as water wherein small gaseous bubbles form on inside surfaces of a container for the liquid and the bubbles then disengage themselves and are carried to the top of the liquid. In this manner, a practically continuous layer of liquid is always in contact with the surface of the container. Film boiling, however, differs from nucleate boiling in that the heat input into the container of fluid is so great that all of the small gaseous bubbles that form on the interior of the fluid container cannot escape from the surface and therefore they unite to form a continuous gaseous interlayer between the fluid and the container. When this occurs, a gaseous insulating layer is formed and the quantity of heat carried of by the water drops markedly and the temperature of the container will start to rise rapidly.
U.S. Pat. No. 3,468,654 recognized the problem of film boiling in a closed system utilizing continuously circulating low velocity cooling water, and proposed to overcome such problem by periodically supplying high velocity cooling water to purge the film from the forming wall so that nucleate boiling could again be accomplished.
Other forms of liquid cooling of mold parts include the use of molten metals such as shown in U.S. Pat. Nos. 3,258,324 and 3,285,728, however although the liquid metal cooling is self-contained within the mold parts, both references require the addition of exteriorly coupled recirculating water so as to cool the liquid metal and condense any vapors resulting from the boiling of the same. In other words, the liquid metal cooling of the aforementioned patents require rather complex and expensive cooling systems, since auxiliary water cooling and/or water cooled condensers are required in order to control the temperature of the liquid metal coolant.
Accordingly, the present invention has overcome the problems encountered with known systems of a mold cooling including air cooling, water cooling and liquid metal cooling, by providing a completely unique self-contained or enclosed water cooling system which facilitates nucleate boiling of the water coolant and thereby achieves a high rate of cooling through the utilization of the heat of evaporation, while simultaneously inhibiting deleterious film boiling by providing a thermal-siphon effect within the water cooled chamber.